Cnet was a partner in the release of version5 to spread the load of the expected take-up of avast5, not to mention the other major download sites also have it. I'm sure they probably have agreements to distribute and there may well be various requirements about what can and can't be said about the product...

Personally I don't see why they would need to have other sites distributing it, but I'm just an avast user not an employee of Alwil Software.